Erythropoietin resistance has been defined in several ways. In studies that analyzed Eprex® use, authors have utilized a dose cut off point of >200units of Eprex®/kg/week as a reasonable marker of 'true' erythropoietin resistance, or erythropoietin resistance occurring with no obvious cause contributing to a poor Eprex® response. Other authors have used the dose cut point of >300units /kg/week to define erythropoietin resistance. Furthermore, a measure of erythropoietin resistance called the Eprex® dose to hematocrit ratio (Eprex®/Hct) has been used as a continuous variable in some studies and has been shown to be positively correlated with certain markers of erythropoietin resistance.